Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form.Metamorphic rocks form when rocks are subjected to high heat, high pressure, hot, mineral-rich fluids or, more commonly, some combination of these factors.
Igneous rocks form when molten rock (magma) originating from deep within the Earth solidifies.
The chemical composition of the magma and its cooling rate determine the final igneous rock type.
Sand and gravel is usually mined in surface pits or rock is crushed to size, gold is mined in surface pits, underground mines, and in streams and rivers.
Igneous rocks include granite (made of crystals of quartz and feldspar, mixed with other minerals).
When buried, the sediments lose water and become cemented to form rock. Clastic sedimentary rocks are the group of rocks most people think of when they think of sedimentary rocks.